Patent GB-1056679-A (GB)
Title: Improvements in hydraulic braking systems
Inventor: RATH HEINRICH BERNHARD
IPC: B60T11/224
Filed: 1964-08-18
Abstract: 1,056,679. Hydraulic brakes. GIRLING Ltd. Nov. 17, 1965 [Aug. 18, 1964], No. 33665/64. Heading F2F. In an hydraulic braking system fluid under pressure is supplied to a brake cylinder or cylinders on a vehicle from an auxiliary cylinder 16 in which works a floating piston 17 which is exposed over the whole of its area to pressure produced by a master cylinder 11 so long as that pressure is below a predetermined value, but is exposed over only a part of its area to the master cylinder pressure when the predetermined limiting value of that pressure is exceeded. Fig. 2 shows the inoperative state of the apparatus in which the master cylinder piston 12 is in its retracted position to allow the recuperation valve 35 to be opened and allow open access, via passages 34, 36, 37, to the reservoir 38. In this position the floating piston 17 abuts against a stationary spigot portion 19 under the effect of a spring 39 provided in the auxiliary cylinder 16. A pressure sensitive valve 25 provided in a bore 23 is opened in this condition by the provision of a spring 30. When the master cylinder piston 12 is advanced by operation of the brake pedal (not shown), the recuperation valve 35 closes and liquid under pressure is forced from the master cylinder to the slave cylinders of the front wheel brakes via connection 14. Master cylinder pressure is also supplied to the annular space 29 in the auxiliary cylinder around the stationary spigot 19 via passageway 15 and via passageway 28 through the open pressure sensitive valve 25, passage 22 and axial passage 21 in the spigot 19 to a recess 18 in the floating piston 17. The master cylinder pressure is thus applied to the whole area of the auxiliary piston 17, the pressure being applied directly to the annular rear end of the piston around the spigot and, through the valve, to the area at the inner end of the axial recess 18. The floating piston 17 is advanced and, after the piston has closed the recuperation ports 37, 36, pressure is built up in the pressure space in front of the piston and is applied to the slave cylinders to the rear wheel brakes via outlet 41. When the master cylinder pressure reaches a predetermined value dependent on the loading of the pressure-sensitive valve 25, that valve closes and cuts off communication between the master cylinder and the axial passage 21 in the spigot so that the master cylinder pressure thereafter is only applied to the annular area of the floating piston 17 around the spigot and the proportion of the total braking effort applied to the rear wheel brakes is correspondingly reduced. Upon release of the brake pedal the pressure in the master cylinder is relieved and a one-way ball valve 33 provided in the pressure-sensitive valve 25 is opened so that liquid in the recess 18 in the auxiliary piston 17 can flow back via the passages 21, 22, 32, 31 and 28 to the annular space 29 and back to the master cylinder while the auxiliary piston 17 and the master cylinder piston 12 return to their inoperative positions. In a modification disclosed in Figs. 6-12 (not shown), a separate pressure-sensitive valve is incorporated in which the spring loading is automatically varied in accordance with the loading of an axle of the vehicle. The loading of the pressure-sensitive valve is varied from the axle through means insensitive to small movements of the axle when the vehicle is in motion, but sensitive to changes in the static position of the axle with changes in the loading of the vehicle.